During the production of high density polyethylene (HDPE) by certain processes e.g. slurry process, a significant quantity is obtained as an off specs low molecular weight (2000-50,000) polymer product commonly known as low polymer wax (LPW) or polymer mud. This low polymer wax is a low value product as it has limited applications and converting these into products like paraffin waxes, microcrystalline waxes, lube and grease base stocks would provide value addition to low polymer wax.
These low polymer waxes are low value products as their low molecular weight does not give them the mechanical strength required for polyethylene and the high melting point does not permit them to be used as substitutes for petroleum waxes. These being polyolefinic in nature do not degrade naturally and may be seen dumped into the factory backyard. Their disposal by land filling or incineration is hazardous to environment as land filling requires an enormous amount of land and results in several problems due to leaching and incineration on the other hand emits toxic gases. Hence for effective utilization of this product there is need for a suitable process that can convert it to useful products. A potential solution is to convert them to products like paraffin waxes or microcrystalline waxes which have multiple industrial and domestic uses or to products like base stocks which can be utilized to formulate lube oils and greases.
Some researchers have tried to convert this type of product into gasoline, diesel and aromatics.
Reference may be made to process developed by Khan et. al (Indian patent application no 0676 DEL 2010) wherein low polymer wax has been converted to gasoline, diesel and aromatics along with LPG by a process comprising of pyrolysis and vapour phase catalytic conversion using zeolite type catalysts. The drawback of this process is that the product is a hydrocarbon liquid having carbon number in the range of C5-C16 and as such waxes and base stocks which have a carbon number greater than 17 could not be obtained. The liquid fuel and aromatics which are produced by this process have different applications.
Reference may be made to the process developed by Eigo et. al (Patent CA 2154799 C, 2002) wherein a method is disclosed that comprises of pyrolysis of polymer in the presence of a higher fatty acid or a hydrochloric acid acceptor or both involving the steps of introducing a reaction mixture resulting from pyrolytic reaction of a polymer in a pyrolysis reactor into an evaporator connected to the pyrolysis reactor at a high temperature, causing the reaction mixture to evaporate in the evaporator while blowing an inert gas into the evaporator, withdrawing volatile components separated from the reaction mixture from the evaporator, and withdrawing the reaction mixture from the evaporator. When the polymer is an olefin polymer, by this method, a pyrolytic wax of quality having satisfactory hue and a minimal content of contaminants is continuously produced in a stable manner for a long period. The drawback of this process is the requirement of higher fatty acid or hycrochloric acid acceptor or both during pyrolysis.
Reference may be made to processes developed by Kumar Anil. (U.S. patent application Ser. No. 12/836,594; Publication no. US 2012/0016169 A1, 15th Jul. 2010 and Indian Patent application No. 0614/DEL/2010 wherein waxes or lubricating grease basestock is obtained from mixed waste plastic wastes like HDPE, LDPE, LLDPE by a process comprising of catalytic depolymerization. The mixed polyethylene waste is preheated to form a molten mixed polyethylene waste. Then depolymerization reaction of the molten mixed polyethylene waste is started. The depolymerization reaction uses a catalyst in a high pressure reactor at a desired temperature using heaters in the high pressure reactor. The catalyst is disposed on a stirring blade. Progression of depolymerization reaction of the molten mixed polyethylene waste is allowed to continue until a pressure in the high pressure reactor reaches a desired value. The heaters are turned off and depolymerization reaction of the molten mixed polyethylene waste is stopped upon the pressure in the reactor reaching desired value. The mixed polyethylene waste is converted to wax or grease base stock.
The drawback of the process is                Requirement of high molecular weight polyethylene as feed stock        Requirement of high temperature (up to 600° C.) and pressure (about 50 psig-350 psig)        Synthesis of a specialty catalyst [Fe—Cu—Mo—P]/Al2O3.        
Reference may be made to process developed by Miller (U.S. Pat. No. 6,822,126) wherein a waste or virgin plastics is converted by continuous process into lube oils. The plastic feed is maintained in a heater at preferred temperatures of 150-350° C. The feed is continuously passed to a pyrolysis reactor preferably maintained at a temperature of 450-700° C. and at atmospheric pressure. Relatively short residence times are employed. Optionally, the reactor effluent is processed in a hydrotreating unit. The effluent is fed to an isomerization dewaxing unit and fractionated to recover lube oil stocks. Preferably, the feed to the pyrolysis reactor can be a blend of waste plastic and waxy Fischer-Tropsch fractions. The drawback of the process is the requirement of hydrogen gas for hydro treating and isomerization dewaxing unit as well as high molecular weight polyethylene and Fischer Tropsch waxes as feedstock.
Reference may be made to process developed by Wall et. al. (U.S. Pat. No. 2,933,536) wherein high molecular weight fluorocarbon polymers including polytetrafluoroethylene (Teflon) have been thermally degraded in the range of 450-480° C. in an atmosphere consisting of a gas selected from the group consisting of IF5 and ClFs into highly stable intermediate polymer compounds such as halogenated greases, waxes and oils having desired fluidity. The drawback of the process is the requirement of a halogenated polymer as a feed as well as halogenated gases and formation of halogenated products.
Reference may be made to the process developed by if Amato et. al. (US patent application no. 20140046102, dated 13 Feb. 2014) wherein a process has been provided for producing a wax from recycled polyethylene, comprising: providing an amount of recycled polyethylene, heating the recycled polyethylene to a high temperature to undergo de-polymerization; degrading the recycled polyethylene to smaller polyethylene fragments; concurrently distilling the recycled polyethylene during the degradation to collect and remove the smaller polyethylene fragments, wherein the recycled polyethylene is converted to the smaller polyethylene fragments having carbon number from about 15 to about 100.
The drawback of this process is the requirement of high molecular weight polyethylene and a concurrent distillation process.